1. Field of the Invention
The present invention relates to a system and a process for recovering ethane and heavier hydrocarbon components from natural gas thereby also generating a gas stream consisting primarily of methane.
2. Description of the Related Art
Many methods currently exist for processing hydrocarbon gas. Some typical examples of isolating and extracting desired components of the higher carbon gas are disclosed in U.S. Pat. Nos. 4,680,042, 4,696,688, 4,832,718 and 4,883,515. These patents generally disclose the removal of a methane rich gas product from an inlet gas stream while also generating a product stream containing ethane, propane, butane, and other heavier hydrocarbon components. The isolation of methane is accomplished by returning a lean solvent from a hydrocarbon product column and injecting the same near the top of an extractor-stripper stripper (ES) column. This lean solvent is used to absorb the heavier hydrocarbon components as a raw gas supplied to the extractor-stripper column. In this fashion the methane rich gas product is removed from the top of the extractor-stripper column.
Additional methods of processing hydrocarbon gas are disclosed in U.S. Pat. Nos. 4,854,955, 4,869,740, 4,889,545, and 5,275,005. These patents all disclose the step of expanding a vapor received from a separator prior to delivering the same to a distillation column.
U.S. Pat. No. 5,325,673 discloses a method of pretreating a natural gas stream using a single scrub column in order to remove freezable C.sub.5 + components. This method consist of feeding a natural gas stream to a feed point on a scrub column operated substantially as an absorption column wherein the heavy components are absorbed from the feed gas using a liquid reflux that is essentially free of such C.sub.5 + components. This patent also teaches that the reflux stream can be overhead vapor condensate having a temperature of about -40.degree. C., or methane-rich liquified natural gas (LNG) or a combination of LNG and vapor condensate.
U.S. Pat. Nos. 4,157,904, and 4,278,457 relate to hydrocarbon gas processing. These patents are concerned with the recovery of ethane and propane from a gas stream in particular a natural gas stream containing carbon dioxide in excess of 0.02 mole percent.
There is still a need for an ethane recovery process which increases the ethane recovery up to a level of about 99% with no increase in plant residue compression horsepower. Alternatively, an improved process could achieve a 96% ethane recovery with approximately a 10% reduction of residue gas compression horsepower. This can result in significant cost savings.